diff --git a/src/Purl/AbstractPart.php b/src/Purl/AbstractPart.php
index 00da252..4b296cc 100644
--- a/src/Purl/AbstractPart.php
+++ b/src/Purl/AbstractPart.php
@@ -224,7 +224,7 @@ public function offsetGet($key): bool
    *
    * @return AbstractPart
    */
-  public function offsetSet($key, $value): AbstractPart
+  public function offsetSet($key, $value): self
   {
     return $this->set($key, $value);
   }
diff --git a/src/Purl/Url.php b/src/Purl/Url.php
index 83f1334..87e0f59 100644
--- a/src/Purl/Url.php
+++ b/src/Purl/Url.php
@@ -86,7 +86,7 @@ public function __construct($url = null, ParserInterface $parser = null)
    *
    * @return Url
    */
-  public static function parse($url): Url
+  public static function parse($url): self
   {
     return new self($url);
   }
@@ -116,7 +116,7 @@ public static function extract($string): array
    *
    * @return Url
    */
-  public static function fromCurrent(): Url
+  public static function fromCurrent(): self
   {
     $scheme = (
         (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off')
@@ -197,7 +197,7 @@ public function setParser(ParserInterface $parser)
    *
    * @return Url
    */
-  public function join($url): Url
+  public function join($url): self
   {
     $this->initialize();
     $parts = $this->getParser()->parseUrl($url);